Support is requested for a study of human temporal bone histopathology to focus on 1) abnormalities of the otic capsule, 2) birth defects of the external, middle and inner ears, 3) congenital deafness, 4) endolymphatic hydrops, 5) head trauma, 6) iatrogenic ear disease, 7) labyrinthine ostosclerosis, 8) sudden deafness and/or sudden hearing loss, 9) tumors, 10) virus infections in the ear, and 11) other ear abnormalities. There is a great need for more knowledge in all of these areas. Knowledge acquired from this study will lead to better understanding of clinical problems and better patient care, not only in otology but also in audiology, nephrology, neurology, oncology, pediatrics, pharmacology, and virology. In addition, studies will be made of the microscopic anatomy and three-dimensional gross anatomy and pathology of human temporal bones. Microscopic studies of various animal temporal bones and fixed intravitally, which do not show postmortem changes, will also be performed to clarify the histopathological findings in human temporal bones which do have postmortem changes. Another objective is to develop new methods and/or devices for processing temporal bones (one of the most difficult of tissues to handle histopathologically) so that the knowedge of temporal bone histopathology gained will be improved in accuracy as well as quality. The human and animal temporal bones are processed for sectioning serially in celloidin-embedded blocks. Every tenth section is stained with hematoxylin and eosin and carefully examined. Surface preparation techniques are also employed whenever needed, particularly in studying the cellular pathology in the cochleo-vestibular end-organs and nerves. We now have 786 human temporal bones from 463 interesting cases available for study or being processed in our laboratory.